Geochemistry of Mesozoic dolerites from Liberia, Africa and Spitsbergen

Mesozoic tholeiitic dolerite dikes that trend northwest-southeast intrude three geologic provinces of contrasting age, lithology and structure throughout northwestern Liberia. Major- and minor-element analyses of thirty-one representative samples show the dolerites to be predominately quartz-normative tholeiitic basalts. Distinct geochemical differences are found to exist between the doleritic intrusions and the geologic province which they intrude. Dolerite dikes that intrude the Paynesville Sandstone exhibit moderately smooth variation trends. These dikes differ from dikes that intrude Precambrian basement rock by being less mafic in character, having higher SiO2 contents, and relatively lower percentages of TiO2, FeOT, MnO and P2o5. Dikes intruding the Pan-African province tend to be more uniform in composition and contain generally higher percentages of TiO2, FeOT, MnO, K2O, and P2O5, and generally lower percentages of Al2o3 and SiO3 and SiO2. (See more in text.)